1. Field of the Invention
The present invention provides a new and improved ceramic insulator and metal weld gear for an improved micro weld head component of an orbital tube welding apparatus.
2. Background Information
Orbital tube welding was first used in the 1960s when the aerospace industry needed a superior joining technique for aircraft hydraulic and fuel system lines. This automated process was accomplished when the arc from a tungsten electrode was rotated accurately around the tubing weld joint. Two decades later orbital tube welding gained application in many other industries due to the development of smaller, more portable, solid-state power supplies, advanced control systems and other advancements. Advancements in orbital welding can now yield controlled, consistently high-quality and well-documented welds cost-effectively.
An orbital welding system consists of a solid-state power supply (operating from 110 VAC) and a rotor and electrode housed in the orbital weld head. The power supply and microprocessor technology system supplies and controls the system's output characteristics, i.e., welding parameters, like the arc welding current, the power to drive the motor in the weld head, and the switching on and off of the shield gas, are programmed.
In automatic orbital welding systems, tubes or pipes are clamped in place. This orbital welding process uses the Gas Tungsten Arc Welding (GTAW; also referred to as TIG welding) process as the source of the electric arc that melts the base material and forms the weld. (The heat found at the tungsten tip can be between approx. 2400 to 2800 degrees F.) The electric arc is established between the non-consumable tungsten electrode (typically two percent thoriated Tungsten or two percent ceriated Tungsten) and the part to be welded, called the weld puddle. To initiate the electric arc, an RF or high-voltage signal ionizes the shielding gas (usually argon) to start a path for the weld current. A capacitor delivers current into the arc to reduce arc voltage to a point where the power supply can regulate. Failure to establish the proper arc gap can compromise weld quality and penetration. The power supply provides the weld current to keep the arc established. The metal or stainless steel tube or pipe to be welded is melted by the intense heat of the arc and fuses together.
The orbital weld head rotates the tungsten electrode and the electric arc around the weld point to join the adjoining surfaces. Orbital weld heads are usually of the enclosed type with an inert atmosphere chamber that surrounds the weld joint. An inert shielding gas, most commonly argon, is fed through the weld head (or torch). Shield gas is required during welding to protect the electrode, molten weld puddle and solidifying weld metal from atmospheric contamination.
Orbital welding equipment is now used by many industries, from non-critical to high purity applications, including semiconduction and pharmaceutical applications. Automated orbital welding equipment can drastically outperform manual welders qualitatively and quantitatively and consistently yield a much higher quality of weld without the normal variability, inconsistencies, errors or defects of manual welding. Also, orbital welding may be used where a tube or pipe to be welded cannot be rotated or readily rotated, or where space restrictions limit the physical size of the orbital welding equipment.
Due to the increasing demand for quality welds it's important to precisely control the travel speed and concentricity of the tungsten tip with the tubes being welded. The moving parts are subjected to intense heat that causes the parts to expand and the weld head needs to allow for this expansion. In the industry today the weld head is either water cooled or air cooled, which helps cool the moving parts and allows for increased duty cycle.
The typical duty cycle is 1 weld every 3-4 minutes. The current weld heads use a plastic housing to insulate the ground (−) current from the positive (−) current. The welding gear is constructed of metal and insulated with plastic and the clamps are metal as well. As the weld is performed the C-shaped gear begins to heat up and expand at the points of the “C”. Expansion can be as much as 0.015″. This expansion causes the tungsten travel path to be oval around the tubes to be welded. The tungsten gap changes as the weld gear heats up and causes inconsistent weld thickness.
The weld gear is driven by 2 spur gears and also is supported by a plastic boss that rides on both the inside and outside diameter of the weld gear. The use of plastic as an insulator limits the duty cycle and does not expand at the same rate of the metal parts, making it difficult to closely align the mating moving parts. When the weld head is used more then the recommended duty cycle the gear expands beyond the calculated tolerance and binds between either the spur gears that drive the weld gear or the boss that support the weld gear. When this happens the gear stops moving and causes a bad weld or breaks the internal drive components.
Another common problem found with the current design is an arcing between the weld gear and the collets that hold the tubes. The inherent shapes of gears have fine points at the tip of the gear tooth design. Because the electrical current passes through the gear to the tungsten tip, the electrical current also passes through the gear tooth. As the tungsten becomes oxidized and worn from use, the electrical current finds more resistance at the tungsten tip than the gear tooth. This causes arcing from the gear to the collets, instead of arcing between tungsten to tube. When this arcing occurred, it is very destructive to the components of the weld head and fixture block as well as the tubing being welded.
In addition to erratic arcing, other problems known to be commonly associated with current orbital welding processes include arc wandering, difficult arc starting, excessive electrode consumption, and oxidized weld deposit.
Another significant problem that has plagued automatic orbital tube welding involves the plastic insulator/housing, which holds all the parts together in an orbital weld assembly. The plastic has a different thermal expansion rate than the metal welding gears. This differential translates into a sloppy fit between the gear and the plastic.
The present invention provides a new and improved ceramic insulator and metal weld gear for an orbital welding apparatus, which overcomes the above-referenced problems and others.